In drive slip control systems the bias pressure for controlling the pressure at the brake is produced by means of a hydraulic unit which contains a motor-driven, valve-controlled pump. It is possible to use for this purpose, for example, the return pump of an antilock control system (U.S. Pat. No. 4,900,102). Antilock control systems are also known in which the bias pressure needed for raising the pressure in ABS controls is produced by means of a hydraulic pump unit and is made available to the ABS control by means of a pressure feed valve (U.S. Pat. No. 4,575,160). The pressure was formerly limited by means of hydraulic limit valves, wherein an electric current proportional to the motor torque under load or a speed proportional thereto is established. U.S. Pat. Nos. 4,900,102 and 4,575,160 are incorporated herein by reference.